JPH10510793A - Vitrification mixtures for fine glass - Google Patents

Abstract

  (57) [Summary] The glass has a chemical composition (% by weight) in the following ranges: silica 50-58, potassium oxide 0-13, sodium oxide 0-9, lithium oxide 0-4, calcium oxide 0-3, magnesium oxide 0-4. Boric anhydride 0-2, zinc oxide 16-30, barium oxide 0-12, titanium oxide 0-6, zirconium oxide 0-5, yttrium oxide 0-5, alumina 0-3, tin oxide 0-5, oxidation Lanthanum 0-9, niobium oxide 0-9, bismuth oxide 0-12, germanium oxide 0-5.

Description

DETAILED DESCRIPTION OF THE INVENTION vitrification mixture TECHNICAL FIELD The present invention for high level glass relates to a glass composition having the characteristics of lead crystal without the presence of lead. 2. Description of the Related Art Lead crystals are well known as glasses that are particularly characterized by exceptional brightness, refractive index, density and sound. According to the definition given by EEC Standard 69/493, adopted in Italian Law No. 827 of 26/11/73, Appendix b, columns e and f, line 2, for glass called "lead crystal" Must have a density of at least 2.90 g / cm ³ and a refractive index of at least 1.545 in addition to containing at least 24% lead. These properties are ensured by the lead content, and the high lead content imparts good workability, sound and gloss to the glass. The need to develop new glasses with the same properties as crystal glass stems from the fact that lead has already been expelled from some manufacturing processes, because lead is potentially toxic, Restrictions on lead use may be expanded as needed in the near future. For this reason, alternative methods have been developed to obtain glasses that do not contain lead but have the physical properties of "crystal glass" described above. To achieve this alternative, a mixture of elements such as barium zinc, calcium, strontium, bismuth, titanium and the like, which are non-toxic and increase density and refractive index values, can be used in place of lead. However, along with these properties, many of these elements are expensive and also impair the workability and color of the glass, so their use is unsuitable for industrial use. Researchers therefore worked to determine the most favorable composition to obtain a lead-free "crystal" having properties suitable for both craft operations and industrial processing, for example as given in the following table. Examples are glasses which have a different composition and which are the subject of International Patent Application WO 93/16964 under the name of the company Compagnie des Cristaller-ies de Baccarat. This composition is characterized in that a mixture of zinc, strontium and calcium is used instead of lead, and the corresponding glass has a satisfactory density and refractive index, but does not have a high melting point and softening point and continuous melting. It has proven difficult to process due to having a suitable devitrification temperature. Another lead-free crystal glass has the composition shown in the following table and is the glass found in European Patent Application Publication No. 0594422A1 under the name of Toyo Glass. According to this European patent, a mixture of barium, zinc, titanium and boron is used instead of lead, the glass having satisfactory physical variable values, especially density and refractive index, at a reasonable cost. However, glasses having the chemical composition shown in this table can be decolorized and difficult to work with due to the high titanium content. DISCLOSURE OF THE INVENTION In order to overcome the disadvantages of known lead-free glasses, according to the present invention, compositions for vitriflable mixtures were created according to the following Table 1: In this composition, instead of lead, a mixture comprising mainly zinc and in addition barium, lanthanum, niobium and bismuth is used, with a total content of said elements ranging from 26% to 33%. Gives an oxide of The sum of these oxides, excluding zinc oxide, must be between 7 and 14%, and furthermore, in order to further improve the chemical resistance and the refractive index of the glass, zirconium, yttrium and titanium are reduced to less than 6% It can be added in the total amount of oxide. Further constituents defining the mixture of oxides forming the glasses of the invention are as follows: (a) The total weight content of SiO ₂ and Al ₂ O ₃ is 52 to ensure sufficient chemical resistance. (B) the total weight content of potassium, sodium and lithium oxides is 12% to 18% to improve processability and fusibility; (c) potassium oxide and sodium oxide Is between 0.9 and 2 to keep the transfer of heavy metal ions low; (d) oxidation of arsenic, antimony, nickel, cobalt, manganese, erbium, neodymium, selenium and cerium as nefining agents and decolorizing agents (E) alumina and oxides of calcium and magnesium to increase the hydrolysis resistance in a total amount of 4% or less; (f) the desired density and Be present tin and germanium in 5 wt% or less of the total amount to achieve the Oriritsu. Within the range of possible compositions in the above-mentioned ranges, the following glasses have particular utility: A) Glasses having compositions in the ranges given in Table 2 below: These figures correspond to glasses having a density and refractive index equal to or greater than those specified by the aforementioned EEC standard at a reasonable cost and having good chemical resistance, for example lead crystal. The following glasses (Table 2/1) can be used as substitutes: More specifically, the following table (Table 2/2) shows the composition of glass having a composition in the range defined in Table 2/1 and measurements of some variables: In this table and in the following tables, the property values for the various glasses are annotated as follows: "DIN 12111" is the chemical resistance value measured according to the German Industrial Standard; "d" is the ASTM standard C729. be a density measured by -75 (kg / dm ^3); "α" is a thermal expansion coefficient value by UNI standard 7460 in the range of ^{0~300 (℃ -1 × 10 -6)} ; "Tg" glass “Mg” is the softening temperature (° C.); “Abbe No.” is the numerical value of the expression (n _D −1) / (n _F −n _C ), and the Abbe number is the optical This is a dispersion index, and corresponds to an increase in the dispersion when the value of the dispersion index is low. B) Compared to the above glasses, the barium content is lower and has better properties, ie physical variables such as acoustics and dispersion are equal or better, but much more expensive, the following limited composition ranges (Table 3) ) By glass: The following table (Table 3/1) shows two ranges of composition according to this last-named limitation: More specifically, Table 3/2 given below gives measurements of the compositions and some variables of two glasses having compositions in the ranges defined in Table 3/1: It can be seen from the above two examples that the optical dispersion increases when bismuth is simply substituted for barium. Tests performed have shown that, when properly combined with various oxides, lead may enjoy one or more of the following properties depending on the situation: inexpensive products, processability, color and optical dispersion. A variable value comparable to that of a crystal can be achieved. Furthermore, the above composition ranges can produce glasses with improved optical properties, high density and considerable chemical resistance without the use of potentially toxic or contaminating elements: The following ranges define compositions that are particularly useful from an industrial manufacturing and / or market standpoint. The above embodiments are merely provided to actually demonstrate the present invention, and it is intended that the present invention be modified without departing from the scope of the concepts defined herein.

────────────────────────────────────────────────── ─── Continuation of front page    (81) Designated countries EP (AT, BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, M C, NL, PT, SE), OA (BF, BJ, CF, CG , CI, CM, GA, GN, ML, MR, NE, SN, TD, TG), AP (KE, LS, MW, SD, SZ, U G), AM, AU, BB, BG, BR, BY, CA, C N, CZ, EE, FI, GE, HU, IS, JP, KE , KG, KP, KR, KZ, LK, LR, LT, LV, MD, MG, MN, MW, MX, NO, NZ, PL, R O, RU, SD, SG, SI, SK, TJ, TM, TT , UA, UG, US, UZ, VN

Claims (1)

Claims 1. A lead-free glass having a density of not less than 1.2.9 g / cm ³ and a refractive index of not less than 1.545, containing various oxides (% by weight) within the range shown in the following table, , Mn, Nd, Er, Co, Sb, As, Se and Ce total less than 2% by weight of oxides of other trace elements: Lead-free glass characterized in that: 2. The following chemical composition (% by weight): 2. A glass according to claim 1, characterized in that it contains a further oxide of a trace element as an impurity or a bleaching agent so as to obtain a physical variable value in the crystal range at a reasonable cost. 3. Chemical composition within the following ranges: 3. The glass according to claim 2, wherein said glass further comprises another oxide of a trace element as an impurity or a decolorizing agent. 4. Chemical composition (% by weight) within the following limits: And containing other oxides of trace elements as impurities or bleaching agents so as to obtain a glass of even better quality than the quality of claim 2 at the expense of a considerable increase in costs. The glass according to claim 1, 5. The following chemical composition values: 5. The glass according to claim 4, wherein said glass further comprises a trace element other oxide as an impurity or a decolorizing agent. 6. A lead-free glass having physical properties that largely correspond to the physical properties of lead crystals, and having an overall chemical composition as described above.